Brake problems!! I need help!
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Junior User
Joined: May 2005
Posts: 96
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From: cold ole' minnesota
Brake problems!! I need help!
A brake problem that is really getting to me.
I will start with all the information leading up to this situation...
I was hauling a heavy load of lumber to the cabin with my rig (in my signature) when I hit the brake and they felt a bit mushy. I got out and checked around a bit and one of the lines that runs from the master cylinder to the proportioning valve on the frame rail had busted open (rusty). I was in the middle of a 400 mile one way trip so I decided to be clever and use a vise grip and pinch this line off. I cut through what was remaining and slowly crimped it down for about an inch. This stopped the leak completely. I figured this way I would have at least one set of brakes.
As soon as I got to driving again, the brakes were nearly impossible to depress. No matter how hard I hit the brakes the truck slowed down very slowly. (not good). I think, and correct me if I am wrong, this is because I had about a 2 foot section of brake line leaving the master cylinder that's was pinched/blocked off so the piston in the cylinder couldn't travel very far. Does this sound right?
I nursed it home, and replaced the line and bled the brakes to get all the air out of it. It took a while to get the air out, but I am confident it is all out of the system now.
Problem is, my brakes are still very mushy. No matter how hard I try to press the brakes the truck does not slow down very fast. On gravel I cannot lock up any of the tires. The ABS light is not on but the brake light remains on.
I am wondering if it possible to damage the master cylinder? Or is the proportioning valve stuck? What could be going on?
Also,
How much vacuum should the vacuum pump be making (the pump that drives the master cylinder power assist?
Thanks in advance, and sorry for the long post, but I need help!
I will start with all the information leading up to this situation...
I was hauling a heavy load of lumber to the cabin with my rig (in my signature) when I hit the brake and they felt a bit mushy. I got out and checked around a bit and one of the lines that runs from the master cylinder to the proportioning valve on the frame rail had busted open (rusty). I was in the middle of a 400 mile one way trip so I decided to be clever and use a vise grip and pinch this line off. I cut through what was remaining and slowly crimped it down for about an inch. This stopped the leak completely. I figured this way I would have at least one set of brakes.
As soon as I got to driving again, the brakes were nearly impossible to depress. No matter how hard I hit the brakes the truck slowed down very slowly. (not good). I think, and correct me if I am wrong, this is because I had about a 2 foot section of brake line leaving the master cylinder that's was pinched/blocked off so the piston in the cylinder couldn't travel very far. Does this sound right?
I nursed it home, and replaced the line and bled the brakes to get all the air out of it. It took a while to get the air out, but I am confident it is all out of the system now.
Problem is, my brakes are still very mushy. No matter how hard I try to press the brakes the truck does not slow down very fast. On gravel I cannot lock up any of the tires. The ABS light is not on but the brake light remains on.
I am wondering if it possible to damage the master cylinder? Or is the proportioning valve stuck? What could be going on?
Also,
How much vacuum should the vacuum pump be making (the pump that drives the master cylinder power assist?
Thanks in advance, and sorry for the long post, but I need help!
Junior User
Joined: Apr 2007
Posts: 95
Likes: 0
From: Wolfe City TX
If I remember correctly there should be a reset button on the proportioning valve that will recenter it then you have to bleed the brakes again and it should work. If not get them pressure bleed by one of the shops that have the equipment to pressure bleed the system. Good Luck
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
On the 93 you have a RABs valve........on the frame left foot area... You need to bleed it after both rears are done...... Check electrical connections on the M/C and the foot brake for the red light....... Vacuum pump should give 21"HG at sea level.
If you would like the Vac pump test and 93 RABS info click on my name and email me.
Subject: RABs 93 and Vac test
If you would like the Vac pump test and 93 RABS info click on my name and email me.
Subject: RABs 93 and Vac test
Post Fiend
Joined: Jan 2005
Posts: 8,402
Likes: 10
Sounds like you still have air in the system. If your truck has RABS then I would think the proportioning valve is in the RABS valve block on the inside of the left side frame rail. You can recenter it if necessary by opening a front bleed screw and pressing the brake pedal. Your brake light should then go out. If your booster vacuum was OK before this happened I would think it is still OK.
Post Fiend
Joined: Jan 2005
Posts: 8,402
Likes: 10
The RABS valve only effects the rear brakes so if you have pressure there you are OK. Apologies for previous post. I had been doing some work on a Chevy truck which has a pressure differential switch and it is necessary to open a bleed screw on it to center it. Does not apply to Ford. I still think you need to keep bleeding it.
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
Lazy K the older Ford trucks before RABs have a proportioning valve that requires resetting after bleeding usually.... anytime there was a substantial difference in pressures between the systems it would shift and illuminate the brake light.
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Post Fiend
Joined: Jan 2005
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Apologies yet again. What I should have said in last post was......"Does not apply to your Ford." I`m now wondering about Altzheimers.
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Junior User
Joined: May 2005
Posts: 96
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From: cold ole' minnesota
Update time.
I bled the entire system. Bench bled the M/C, put it back on, and bled the RABS valve, then RR, LR, RABS again, RF and then LF. I bled about a gallon of brake fluid through the system; I cannot find any air anywhere. The pedal feels very firm, and I can apply pressure and it depresses about 2 inches then feels very firm. When I try to drive the truck, I can mash the brakes and the pedal goes almost all the way to the floor, and the truck stops, but very slowly. I cannot lock the tires up on gravel. The red brake light is still on.
Calipers, rotors, drums and shoes are only about 6 months old, (5k miles) and they were on the rig before this problem started and worked fine.
I am going to replace the M/C just to see, but does anyone have any other ideas?
Thanks,
Clint
I bled the entire system. Bench bled the M/C, put it back on, and bled the RABS valve, then RR, LR, RABS again, RF and then LF. I bled about a gallon of brake fluid through the system; I cannot find any air anywhere. The pedal feels very firm, and I can apply pressure and it depresses about 2 inches then feels very firm. When I try to drive the truck, I can mash the brakes and the pedal goes almost all the way to the floor, and the truck stops, but very slowly. I cannot lock the tires up on gravel. The red brake light is still on.
Calipers, rotors, drums and shoes are only about 6 months old, (5k miles) and they were on the rig before this problem started and worked fine.
I am going to replace the M/C just to see, but does anyone have any other ideas?
Thanks,
Clint
Cargo Master
Joined: Feb 2007
Posts: 2,477
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From: Taylorsville, NC
Is this with the engine running but the truck not moving, or engine not running?
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
Rear brakes way out of adjustment can cause your low pedal problem also....... If the vac pump is working correctly, is the booster working .... check the check valve on the booster. To check a M/C, pump the pump quickly several times to see if it rises...... if it does the internal lip seals may be worn allowing a fluid bypass. Remember our vac pump supplies just enough vac for about 4 pumps at higher RPMs..... there is no accumulator to store vacuum on the newer trucks.
Thread Starter
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Junior User
Joined: May 2005
Posts: 96
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From: cold ole' minnesota
Good news. I have good brakes now!
1. Replaced the M/C - brakes got a little better, no fading to the floor anymore.
2. Tightened rear brake pads, both way out of adjustment, brakes improved a lot.
3. Measured vacuum from pump, only at 7 in hg, replaced vacuum pump, now brakes work great. Perfect response, very easy to push, anit-locks in rear work great, truck stops on a dime!
Thanks again for everyone’s help!
1. Replaced the M/C - brakes got a little better, no fading to the floor anymore.
2. Tightened rear brake pads, both way out of adjustment, brakes improved a lot.
3. Measured vacuum from pump, only at 7 in hg, replaced vacuum pump, now brakes work great. Perfect response, very easy to push, anit-locks in rear work great, truck stops on a dime!
Thanks again for everyone’s help!
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